It has long been known to enhance the comfort, convenience and utility of telescopes, binoculars and other such optical apparatus by providing these devices with an eyeguard to interface between the user's eye and the optical instrument. Eyeguards often take the form of a flexible rubber rim or cup extending from the eyepiece of the optical instrument. The eyeguard typically allows the user to comfortably position his eye against the instrument, assists the user in maintaining the proper eye relief distance, (i.e., the distance from the eye lens of the optical instrument to the user's eyeball) to provide the user with full field of view, and to shield the user's eye from ambient or reflected light which may distract from the image transmitted through the optical instrument.
The exposed lenses of optical instruments are often coated with specialized compounds ("optical coatings" ) which serve to improve the optical characteristics of the instrument. However, these optical coatings are frequently vulnerable to contamination or damage by airborne dirt, lint, dust, or oils, which may accumulate on the exposed lenses of the optical instrument and degrade the performance of the optical coatings. Conventional rim or cup type eyeguards provide little if any protection against such contamination of the lenses at the eye end of an optical instrument. Lens caps or covers which fit over the eyeguards are well known and provide good protection, however, the user must remember to put them in place after each use. A need exists, therefore, for an eyeguard which automatically protects the eye-end lenses of an optical instrument against dirt, dust or other airborne contaminants without conscious action by the user.
Enhanced vision devices are a type of optical instrument which are finding increasing use in military, law enforcement, and civilian applications. Enhanced vision devices employ light amplification, infrared or thermal imaging, or other technologies to provide visible images under low light or smoke-obscured conditions under which normal optical instruments would be ineffective. Examples of enhanced vision devices include night vision goggles, starlight scopes, and thermal sights. Such devices find a wide range of applications including personnel mounted night vision goggles, rifle mounted sniper scopes, and vehicle mounted thermal sites.
While the lenses of enhanced vision devices are subject to contamination by airborne particles just as are conventional optical instruments, the unique nature of some enhanced vision devices presents some additional problems. For example, some night vision devices employ photosensitive materials which may be damaged by exposure to high light levels. Such devices may be rendered temporarily unusable or even permanently damaged if sunlight or other strong lights are allowed to enter the instrument through the eye lens. Conventional rim or cup type eyeguards provide very limited protection against the unintended entry of light into the eye lens of an optical instrument. Some devices may be equipped with lens caps or covers which the user can place over the lens when the lens is not in use, thereby protecting it from the unintended entry of light. However, the effectiveness of such lens caps is completely dependent upon their consistent use by the user. It is difficult to ensure the consistent use of such caps in many situations such as combat or law enforcement situations. A need exists, therefore, for an eyeguard which prevents the entry of light into the eye lens of an optical instrument when it is not being used.
The use of enhanced vision devices at night or in other circumstances of darkness presents yet another problem for conventional eyeguards, especially when used under circumstances involving personal danger such as combat or law enforcement activities. When an enhanced vision device is being used, a light image is transmitted through the eyepiece. This image enters the eye of the user when he looks through the instrument. However, when the user moves his eye back from the eye-end of the instrument, the light image will continue being projected back through the end of the instrument, and is commonly seen as a bright spot or glow on the face of the user. This reflected light may serve to disclose the otherwise concealed position of a soldier or other concealed person. Conventional rim or cup type eyeguards provide little protection against the undesired escape of light from the eyepiece of an optical instrument. A need exists, therefore, for an eyeguard which automatically prevents the escape of light from the eyepieces of an optical instrument when it is not in use.
Eyeguards having an internal diaphragm which opens and closes automatically are known. Devices such as the CMI SB0525-A comprise a dome-shaped instrument portion, a cone-shaped forcing cone, with a segmented diaphragm there between. The dome shaped instrument-end was affixed to the eye-end of the optical instrument to be used. The diaphragm consists of a disk of material positioned within the dome shaped instrument portion of the eyeguard, such that the diaphragm extends perpendicularly across the line of sight through the optical instrument. A plurality of radial cuts are made in the diaphragm disk, resulting in a diaphragm comprising a plurality of wedge-shaped portions, each joined at its wide end to the interior of the dome-shaped instrument portion of the eyeguard. In its normal, relaxed state, the segments of the diaphragm will prevent dust, dirt or other contaminants from reaching the eye lens of the optical instrument. Similarly, the diaphragm will prevent the escape of light from the eye lens of the optical instrument. When the user positions the eyeguard against the periocular (i.e., around the eye) portion of his face and pushes towards the eye-end of the optical instrument, the forcing cone portion of the eyeguard will move forward, pushing against the back side of the diaphragm segments and, in turn, forcing them to move forward and outward, thus clearing a path for light to be transmitted through an opening in the center of the forcing cone. When the user removes his eye from the eyeguard, the natural resilience of the flexible eyeguard causes the forcing cone to return rearward to its original position and causes the diaphragm to close automatically, thus protecting the eye-end lens of the optical instrument from contamination, and preventing the passage or entry of light into the optical instrument. Prior art diaphragm-equipped eyeguards, such as the CMI SB0525-A, while addressing some of the problems of rim and cup type eyeguards, nevertheless have proven unsatisfactory for at least two reasons. First, excessive force was required to activate the diaphragm of prior art eyeguards. Some prior art eyeguards required the user to exert a force of 72 ounces to initially open the diaphragm and a force of 35 ounces to maintain the diaphragm in the open position. These values of force were unsatisfactory, as they tended to distort the vision of the user, and cause fatigue, eye strain or headaches during extended use. A need exists, therefore, for a diaphragm equipped eyeguard requiring low force levels to initially open the diaphragm and to maintain the diaphragm in the open position, yet which reliably closes when the user removes his eye from the eyeguard.
The second drawback with prior art diaphragm-equipped eyeguards is that excessive eye travel is required to fully open the diaphragm. For example, prior art eyeguards required from about 0.5 inch to about 0.75 inch travel to fully open the diaphragm. Eyeguards designed to allow such long travel sometimes prevented the user from achieving the proper eye relief, thus restricting the field of view through the optical instrument. A need exists, therefore, for a diaphragm-equipped eyeguard requiring reduced eye movement to fully open the diaphragm.